In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.
Because of the good ratio of stiffness and strength to density they exhibit, composite materials and particularly sandwich components are used widely in aircraft construction. Such composite materials, for example core structure textile materials or other core composites, are generally constructed from an upper and a lower cover layer or surface layer, between which a honeycomb-like core structure consisting of vertically oriented cells having a hexagonal cross section may be positioned to increase the structure's stiffness.
The multifunctionality of foams renders them of interest for use in core composites for large structural elements, e.g. in aviation applications, both for the manufacturing of components and with regard to the enhanced properties of the components themselves. For reinforcement of the foam-based core composites, certain sewing techniques are used with which it is possible to incorporate fibres or threads referred to in the following as semi-finished textile products in hard foam components. Following a resin infiltration process, the zones through which the fibres pass then increase the mechanical reinforcement of the foam.
The fibres or threads that are added for reinforcement may be in the form of “rovings”, which consist of fibres in parallel alignment, or they may be threads, which consist of twisted or wound fibres.
In known sewing methods, initially a needle is inserted into the foam, and passes through it. The needle brings the thread into the foam at the same time. In this operation, while it is being inserted in the foam, the thread extends parallel to and substantially over the entire length of the needle. The size of the perforation hole is thus determined by the diameter of the needle and the thickness of the thread.
After the needle has been withdrawn from the foam or textile, a hole remains the diameter of which is relatively large compared with the diameter of the thread that is introduced. This results in that, after the infiltration with a resin the area of the hole that is not occupied by fibres is filled with resin, which can add to the weight of the finished component.
DE 10 2005 024 408 A1 describes the reinforcement of foam materials by means of a knotting process, in which the needle first passes through the material to be reinforced (the foam material) and only then picks up the semi-finished textile product in the area of the foam material underside, and then pulls it through the perforation with the subsequent backwards movement.
This technique enables the hole diameter to be kept relatively small.